December
17, 2018, Ecological Society of America
When a
caterpillar disguises itself as a snake to ward off potential predators, it
should probably expect to be treated like one.
This is
exactly what happened in Costa Rica earlier this year, when researchers
witnessed a hummingbird defending its nest from what it interpreted to be
a snake,
but was actually a larva of the moth Oxytenis
modestia. The encounter is described in a new paper published in the
Ecological Society of America's journal Ecology.
These
moths—sometimes called the dead-leaf moth or the Costa Rica leaf moth—resemble
flat dried leaves as adults. The caterpillars can
inflate the top of their heads to expose a pair of eyespots. When disturbed,
they raise their head up and move from side to side, increasing the snake-like
appearance. In particular they resemble a green parrot snake, known to prey on
nesting birds.
The
attacking hummingbird's nest with eggs was about 10cm away from the caterpillar
in a small tree. When the researchers went to look for an assumed snake, they
instead found the caterpillar feeding on a leaf immediately above the nest.
"Hummingbirds
have a few stereotypical styles of flying: visiting flowers, preying on swarms
of tiny insects, chasing each other, and mating/territorial display
flights," says lead author James H. Marden, professor with the Department
of Biology at Pennsylvania State University. "Mobbing behavior directed
against a threat to their nest is much less common but distinct and easy to
recognize if you know their other flight behaviors... One can recognize this
from a distance and only notice the source of their agitation upon close
inspection."
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